This application claims priority under 35 U.S.C. xc2xa7xc2xa7 119 and/or 365 to Appln. Ser. No. 199 59 342.6 filed in Germany on Dec. 9. 1999; the entire content of which is hereby incorporated by reference.
The present invention relates to the field of power plant technology. It concerns a heat-recovery steam generator, in particular for a gas-turbine plant of a combined-cycle power plant, according to the preamble of claim 1.
Publication DE-A1-197 44 917, for example, has disclosed such a heat-recovery steam generator.
In the case of heat-recovery steam generators (HRSG) or heat-recovery boilers which, for example, are arranged downstream of the gas-turbine plants in combined-cycle power plants and generate steam for a steam turbine by means of the hot flue gases of the gas turbine, purging of the heat-recovery steam generator with air before restarting the plant after an interruption in operation is specified in normal practice and for safety reasons. This is intended to safely remove any residues of unburned fuel in the heat-recovery steam generator and thus avoid, for example, undesirable self-ignition.
The air required for the purging operation is provided by the gas turbine itself. To this end, the gas turbine is driven by the generator, operated as an electric motor, and draws in air with the compressor part and delivers the drawn-in air through the heat-recovery steam generator. Since the free cross section of flow of the heat-recovery steam generator is relatively large compared with the mass flow produced in this way by the gas turbine, only comparatively low flow velocities can be achieved by this type of purging. The result of this is that either the purging is incomplete or has to be carried out for a longer period.
To solve these problems, it has been proposed in publication DE-A1-197 44 917 mentioned at the beginning to subdivide the free cross section of flow of the heat-recovery boiler into a plurality of parallel flow passages which can be selectively shut off by means of a shut-off arrangement. In this way, by shutting off some of the flow passages, the cross section of flow in the boiler can be reduced to a fraction during the purging andxe2x80x94at the same air mass flow from the gas turbinexe2x80x94the flow velocity of the purging air can be increased considerably. In this case, rotary slide valves are used as the shut-off arrangement, these rotary slide valves being arranged at the foot of the exhaust-gas chimney on a central drive shaft. A disadvantage with this solution is that an independent, additional and mechanically complicated shut-off arrangement has to be provided there only for the purging operation.
The object of the invention is therefore to provide a heat-recovery boiler which, without additional outlay, permits rapid and reliable purging at a limited cross section of flow and thus increased flow velocity of the purging air.
This object is achieved by all the features of claim 1 together. The invention is based on the fact that, on account of the increasingly stricter exhaust-gas regulations, the use of catalyst apparatuses in the heat-recovery boiler for the further reduction of, for example, nitrogen oxides and carbon monoxide is virtually obligatory. In the case of such catalyst apparatuses, it is normal practice, for example, to provide an absorption layer of potassium carbonate, by means of which the nitrogen oxides present can be converted into potassium nitrites and potassium nitrates. Since the absorption layers are exhausted during this conversion, the catalyst apparatuses have to be regenerated at regular intervals. To this end, the catalyst apparatuses are subdivided into individual catalyst sections which, for regeneration during operation, can be closed individually on the inlet side and outlet side by shut-off means such as flaps or the like. A suitable gas mixture which regenerates the absorption layers is then directed through such a closed-off catalyst section via special feed lines. The essence of the invention, then, is to also use the shut-off devices which are present anyway in such a catalyst apparatus for shutting off individual flow passages during the purging operation. In this way, it is possible to achieve effective and reliable purging of the heat-recovery boiler without additional constructional outlay.
In this case, it is conceivable for the number of flow passages to be equal to the number of catalyst sections, and for one of the catalyst sections to be allocated to each of the flow passages. However, it is also just as conceivable for the number of catalyst sections to be a multiple of the number of flow passages, and for a plurality of catalyst sections to be allocated to each flow passage.
The construction of the heat-recovery steam generator is especially simple if it is constructed in a modular manner from a plurality of heat-exchanger modules arranged one behind the other, and the catalyst apparatus is designed as a catalyst module.
The invention is to be explained in more detail below with reference to exemplary embodiments in connection with the drawing, in which:
FIG. 1 shows the side view of a heat-recovery steam generator of modular construction, having vertical heating surfaces and a catalyst apparatus connected in between, as is suitable for realizing the invention, in perspective representation;
FIG. 2 shows the side view of a catalyst apparatus consisting of individual catalyst sections provided with shut-off means, as is suitable for realizing the invention, in perspective representation;
FIG. 3 shows the internal construction of a catalyst apparatus according to FIG. 2 in plan view;
FIG. 4 shows an allocation of catalyst sections and flow passages in a first exemplary embodiment of the invention; and
FIG. 5 shows an allocation of catalyst sections and flow passages in a second exemplary embodiment of the invention.